The present invention is directed, in general, to an optical device and, more specifically, to a micro-electro-optical mechanical device having an implanted dopant included therein and a method of manufacture therefor.
Optical communication systems typically include a variety of optical devices, for example, light sources, photo detectors, switches, cross connects, attenuators, mirrors, amplifiers, and filters. The optical devices transmit optical signals in the optical communications systems. Some optical devices are coupled to electro-mechanical structures, such as thermal actuators, forming an electro-mechanical optical device. The term electro-mechanical structure, as used herein, refers to a structure which moves mechanically under the control of an electrical signal.
Some electro-mechanical structures move the optical devices from a predetermined first position to a predetermined second position. Cowan, William D., et al., xe2x80x9cVertical Thermal Actuators for Micro-Opto-Electro-Mechanical Systems,xe2x80x9d SPIE, Vol. 3226, pp. 137-146 (1997), describes one such electro-mechanical structure useful for moving optical devices from the predetermined first positions to the predetermined second positions.
These micro-electro-mechanical systems (MEMS) optical devices often employ a periodic array of micro-machined mirrors, each mirror being individually movable in response to an electrical signal. For example, the mirrors can each be cantilevered and moved by an electrostatic, piezoelectric, magnetic, or thermal actuation. See articles by L. Y. Lin, et al., IEEE Photonics Technology Lett. Vol. 10, p. 525, 1998, R. A. Miller, et al. Optical Engineering Vol. 36, p. 1399, 1997, and by J. W. Judy et al., Sensors and Actuators, Vol. A53, p. 392, 1996, and U.S. patent applications Ser. No. 09/390,158, filed Sep. 3, 1999, now U.S. Pat. No. 6,392,281, Ser. No. 09/415,178, filed Oct. 8, 1999, now U.S. Pat. No. 6,300,619, Ser. No. 09/410,586, filed Oct. 1, 1999, now U.S. Pat. No. 6,288,821, and Ser. No. 09/197,800 filed Nov. 23, 1998, now U.S. Pat. No. 6,256,430, which are incorporated herein by reference.
The mirrors used in these optical devices are typically made up of a material which reflects light with high reflectivity at the desired operating wavelength of the light, for example at about the 1000-1600 nm wavelength range for the SiO2 optical fiber-based telecommunication systems. Some examples of such reflective materials are gold, silver, rhodium, platinum, copper or aluminum. These reflective metal films typically have a thickness ranging from about 20 nm to about 2000 nm, and are deposited on a movable membrane substrate such as a silicon substrate. At least one adhesion-promoting bond layer is desirably added between the reflecting film and the substrate in order to prevent the reflecting film from getting peeled off. The fabrication of movable membrane structure in MEMS devices is well established and is typically based on silicon wafer processing.
However, such systems have certain disadvantages. For example, when a thin metal film is deposited on a rigid substrate, a tensile or compressive stress is often introduced in the film as well as in the substrate. This is due to a number of different reasons, such as a film-substrate mismatch in the coefficient of thermal expansion (CTE), a mismatch in the lattice parameter, nonequilibrium atomic arrangement in the film, inadvertent or intentional incorporation of impurity atoms, etc. The presence of such stresses tends to cause a variety of dimensional instability problems especially if the substrate is relatively thin, as is the case in the MEMS membranes which usually are only several-micrometers thick. Other examples of the dimensional problems in the MEMS mirror structure caused by the stress include: i) undesirable bowing of the mirror substrate (membrane), which results in a non-focused or non-parallel light reflection and an increased loss of optical signal, ii) time-dependent change in mirror curvature due to the creep or stress relaxation in the reflective metal film, bond layer or the membrane substrate, iii) temperature-dependent change in mirror curvature due to the altered stress states and altered CTE mismatch conditions in the metal film, bond layer, and membrane substrate materials with changing temperature.
For electro-optic devices such as the optical cross connect systems to be reliable and reproducible, the stability of the mirror curvature is imperative. This importance of mirror curvature stabilization has not received much attention in prior art electro-optic devices.
Accordingly, what is needed in the art is an electro-optic device, and a method of manufacture therefore, that does not encounter the stability problems associated with mirror curvature, as experienced in the prior art electro-optic devices.
To address the above-discussed deficiencies of the prior art, the present invention provides a micro-electro-mechanical system (MEMS) optical device. The micro-electro-mechanical system (MEMS) optical device includes a mirror having a substrate with an implanted light reflective optical layer thereover, and a mounting substrate on which the mirror is movably mounted. The inclusion of the implanted dopant within the light reflective optical layer increases the tensile stress of the device and tends to correct the concave curvature of the mirror structure toward a desirably flat configuration.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.